The original 520ST case design was created by Ira Velinsky — Atari's chief Industrial Designer.[17] The ST was basically wedge shaped, featuring bold angular lines and a series of grilles cut into the rear for airflow. The keyboard had soft tactile feedback and rhomboid-shaped function keys across the top. The 520ST was an all-in-one unit, similar to earlier home computers like the Commodore 64. By the time the 520ST reached the market, however, consumers demanded a keyboard with cursor keys and a numeric keypad. For this reason, the 520ST ended up significantly larger than previous popular all-in-one machines like the Commodore 64.

The 520ST used an external "brick" power supply, floppy disk, monitor and mouse. Even basic system setups thus suffered from cable spaghetti, a problem future versions would address to one degree or another. Early 520ST owners became accustomed to the "Atari Twist" and the "Atari Drop" service procedures[citation needed]. The "Atari Twist" seemed to help discharge built-up static electricity (Atari soldered-down the metal shielding to fix the problem) while the "Atari Drop" appeared to help re-seat chips which may have become partially unseated over time.